OFDMA Networks Research Articles

Calculation of the performance measurements for elastic optical OFDM networks

We present an approximate analytical method to evaluate the performance measurements in optical orthogonal frequency-division multiplexing networks. Our approach divides the network into layers, and the equivalent path technique is used to model each path as an equivalent single-link system. The analysis of the performance measurements for an equivalent single-link system is based on a superposition concept using the Kaufman/Delbrouck recursion model. We assume static routing with a first-fit spectrum allocation. The simulation results indicating the accuracy of our method are presented.

Achievable rate maximization for decode-and-forward MIMO-OFDM networks with an energy harvesting relay.

This paper investigates the system achievable rate for the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) system with an energy harvesting (EH) relay. Firstly we propose two protocols, time switching-based decode-and-forward relaying (TSDFR) and a flexible power splitting-based DF relaying (PSDFR) protocol by considering two practical receiver architectures, to enable the simultaneous information processing and energy harvesting at the relay. In PSDFR protocol, we introduce a temporal parameter to describe the time division pattern between the two phases which makes the protocol more flexible and general. In order to explore the system performance limit, we discuss the system achievable rate theoretically and formulate two optimization problems for the proposed protocols to maximize the system achievable rate. Since the problems are non-convex and difficult to solve, we first analyze them theoretically and get some explicit results, then design an augmented Lagrangian penalty function (ALPF) based algorithm for them. Numerical results are provided to validate the accuracy of our analytical results and the effectiveness of the proposed ALPF algorithm. It is shown that, PSDFR outperforms TSDFR to achieve higher achievable rate in such a MIMO–OFDM relaying system. Besides, we also investigate the impacts of the relay location, the number of antennas and the number of subcarriers on the system performance. Specifically, it is shown that, the relay position greatly affects the system performance of both protocols, and relatively worse achievable rate is achieved when the relay is placed in the middle of the source and the destination. This is different from the MIMO–OFDM DF relaying system without EH. Moreover, the optimal factor which indicates the time division pattern between the two phases in the PSDFR protocol is always above 0.8, which means that, the common division of the total transmission time into two equal phases in previous work applying PS-based receiver is not optimal.

Performance Analysis and Optimisation of FFR-Aided OFDMA Networks using Channel-Aware Scheduling

Modern cellular standards typically incorporate interference coordination schemes allowing near universal frequency reuse while preserving reasonably high spectral efficiencies over the whole coverage area. In particular, fractional frequency reuse (FFR) and its variants are deemed to play a fundamental role in the next generation of cellular deployments (B4G/5G systems). This paper presents an analytical framework allowing the downlink performance evaluation of FFR-aided OFDMA networks when using channel-aware scheduling policies. Remarkably, the framework contemplates the use of different rate allocation strategies, thus allowing to assess the network behaviour under ideal (capacity-based) or realistic (throughput-based) conditions. Analytical performance results are used to optimise the FFR parameters as a function of, for instance, the resource block scheduling policy or the density of UEs per cell. Furthermore, different optimisation designs of the FFR component are proposed that allow a tradeoff between throughput performance and fairness by suitably dimensioning the FFR-defined cell-centre and cell-edge areas and the corresponding frequency allocation to each region. Numerical results serve to confirm the accuracy of the proposed analytical model while providing insight on how the different parameters and designs affect network performance.

Energy Efficiency With Proportional Rate Fairness in Multirelay OFDM Networks

This paper investigates the energy efficiency (EE) in multiple relay aided OFDM system, where decode-and-forward (DF) relay beamforming is employed to help the information transmission. In order to explore the EE performance with user fairness for such a system, we formulate an optimization problem to maximize the EE by jointly considering several factors, the transmission mode selection (DF relay beamforming or direct-link transmission), the helping relay set selection, the subcarrier assignment and the power allocation at the source and relays on subcarriers, under nonlinear proportional rate fairness constraints, where both transmit power consumption and linearly rate-dependent circuit power consumption are taken into account. To solve the non-convex optimization problem, we propose a low-complexity scheme to approximate it. Simulation results demonstrate its effectiveness. We also investigate the effects of the circuit power consumption on system performances and observe that with both the constant and the linearly rate-dependent circuit power consumption, system EE grows with the increment of system average channel-to noise ratio (CNR), but the growth rates show different behaviors. For the constant circuit power consumption, system EE increasing rate is an increasing function of the system average CNR, while for the linearly rate-dependent one, system EE increasing rate is a decreasing function of the system average CNR. This observation is very important which indicates that by deducing the circuit dynamic power consumption per unit data rate, system EE can be greatly enhanced. Besides, we also discuss the effects of the number of users and subcarriers on the system EE performance.

Distributed Resource Allocation for Multi-cell Cooperative OFDMA Networks with Decode-and-Forward Relaying

In this paper, the downlink resource allocation is investigated for multi-cell cellular OFDMA networks with relaying, and a low-complexity distributed scheme is proposed. The target is to maximize the system weighted sum rate as well as provide fair services for each class of users. The problem is formulated as a mixed integer programming with the individual power constraints of the base station and relay station. The iterative multilevel water-filling is exploited in the power allocation in each cell, and different cells interact and cooperative with one another implicitly, which reduces the signal overhead and the computational complexity. Furthermore, subcarrier pairing and grouping are also discussed to enhance the system throughput or reduce the signaling overhead. Simulation results show that the algorithm converges fast, and outperforms some traditional schemes in terms of system throughput, and achieves fair and ubiquitous data coverage for heterogeneous users.

On the power allocation strategies in coordinated multi-cell networks using Stackelberg game

In this paper, we study the power allocation problem in multi-cell OFDMA networks, where given the tradeoff between user satisfaction and profit of the service provider, maximizing the revenue of the service provider is also taken into account. Consequently, two Stackelberg games are proposed for allocating proper powers to central and cell-edge users. In our algorithm, assuming the fact that users agree to pay more for better QoS level, the service provider imposes optimum prices for unit-power transmitted to users as they request different levels of QoS. In addition, in order to improve system performance at cell-edge locations, users are divided into two groups based on their distance to the corresponding base-station (BSs): Central users and cell-edge users. The paper also exploits unique features of Coordinated Multi-Point Joint Transmission (CoMP-JT) where coordinated BSs are clustered together statically or dynamically in order to also address the requirements of cell-edge users. After simulating the proposed game with static clustering, a simple dynamic clustering algorithm is introduced for inter-cell coordinated networks where its performance is evaluated through simulations.

Learning to Be Green: Robust Energy Efficiency Maximization in Dynamic MIMO–OFDM Systems

In this paper, we examine the maximization of energy efficiency (EE) in next-generation multiuser MIMO–OFDM networks that vary dynamically over time—e.g., due to user mobility, fluctuations in the wireless medium, modulations in the users’ load, etc. Contrary to the static/stationary regime, the system may evolve in an arbitrary manner, so users must adjust “on the fly,” without being able to predict the state of the system in advance. To tackle these issues, we propose a simple and distributed online optimization policy that leads to no regret , i.e., it allows users to match (and typically outperform) even the best fixed transmit policy in hindsight, irrespective of how the system varies with time. Moreover, to account for the scarcity of perfect channel state information (CSI) in massive MIMO systems, we also study the algorithm’s robustness in the presence of measurement errors and observation noise. Importantly, the proposed policy retains its no-regret properties under very mild assumptions on the error statistics: on average, it enjoys the same performance guarantees as in the noiseless deterministic case. Our analysis is supplemented by extensive numerical simulations, which show that, in realistic network environments, users track their individually optimum transmit profile even under rapidly changing channel conditions, achieving gains of up to 600% in energy efficiency over uniform power allocation policies.

Energy minimization resource allocation schemes for relay-enhanced OFDMA networks

This paper studies the problem of joint allocation of subchannel, transmission power, and phase duration in the relay-enhanced bidirectional orthogonal frequency-division multiple access time division duplex systems. The challenges of this resource allocation problem arise from the complication of multiple-phase assignments within a subchannel since the relay station can provide an additional signal path from the base station to the user equipments (UEs). Existing research work does not fully consider all the influential factors to achieve feasible resource allocation for the relay-based networks. Since energy consumption is one of the principal issues, the energy minimization resource allocation (EMRA) schemes are proposed in this paper to design the allocation of subchannel, power, and phase duration for the UEs with the consideration of UE's quality-of-service (QoS) requirements. Both the four-phase and two-phase bidirectional relaying assignments and the network coding technique are adopted to obtain the suboptimal solutions for the proposed EMRA schemes. Different weights are designed for the UEs to achieve the minimization of weighted system energy for the relay-enhanced networks. Simulation results show that the proposed EMRA schemes can provide comparably better energy conservation and outage performance with QoS support.

Optimal FFR Policies: Maximization of Traffic Capacity and Minimization of Base Station’s Power Consumption

This letter investigates application of optimal fractional frequency reuse (FFR) policies in an OFDMA network of macrocells. Optimality is investigated, first in terms of maximum traffic capacity, the maximum demand in traffic volume per second that can be served by the cell at the session layer. Second, optimality is investigated in terms of minimum total power consumption, applying a dynamic on – off model of power consumption at the base station (BS). The analysis includes the impact of the multicarrier proportional fair (PF) scheduler, providing concise expressions for distribution of active users and for user throughput.

Joint scheduling, queues management and routing aware fairness in a cell downlink network

New generations of cellular networks are expected to meet the exponential evolution of the requirements of the wireless network services. Thus, standards like 3GPP LTE-Advanced and IEEE 802.16m have been developed in different releases in order to fulfil the rather challenging goals. New paradigms such as cooperative relaying, OFDMA access technique and the cross-layer approach have great application potential contributing to this development process. Particularly, these mechanisms are important in macro cell downlink scheduling. Within this paper, two novel algorithms of radio resource management RRM denoted Max-of-Max and Max-deviation are proposed. They are standard-compliant cross-layer mechanism in downlink OFDMA networks. If the reduction of the schemes complexity is a main key of this study, the high ubiquitous cell throughput aware fairness among users remains a fundamental purpose. With the aim to investigate the proposed algorithms performance, a selection of numerical results is outlined.

Energy Optimization in Dense OFDM Networks

Network densification is a promising technology to increase 5G system capacity. Energy saving and resource utility are the key issues for the densified OFDM systems. In contrast with the conventional energy optimization problem for MIMO–OFDM system, we use a more realistic model for SINR by considering the load factor of OFDM systems, which makes the energy optimization problem very difficult to solve. First, we show that for single-antenna scenario, this problem can be transformed into a convex problem, which can be solved more efficiently comparing with the existing methods. Next, for the more complex multiple-antenna scenario, we derive a successively convex program method to obtain the KKT point of this problem. Simulation shows the effectiveness of the proposed method.

Utility-based efficient dynamic distributed resource allocation in buffer-aided relay-assisted OFDMA networks

In this paper, we study resource allocation in buffer-aided relay-assisted OFDMA networks. We consider utility-based stochastic optimization framework where there are constraints to be met either instantaneously or in average sense. Using the well-known Lyapunov drift-plus-penalty policy, we extract the instantaneous problem that needs to be solved in each slot to control the data admission and allocate the time slots, power, and subchannels. We propose the parameters that should be taken into account in utilizing the drift-plus-penalty policy in relay-assisted cellular networks, for providing fair data admission and satisfying the average power constraints. We introduce a low-complexity strategy for power and subchannel allocation and propose distributed and centralized algorithms to utilize it. Specifically, the proposed efficient dynamic distributed resource allocation (EDDRA) scheme is suitable for use in practice as it imposes less overhead on the system and splits the resource allocation tasks among the base station (BS) and the relays. Extensive simulation results show the effectiveness of the proposed parameters in meeting the objective and the constraints of the studied problem. We also show that the proposed EDDRA scheme has close performance to the proposed centralized one and outperforms an existing centralized scheme.

QoE‐ and energy‐efficient resource optimization in OFDMA networks with bidirectional relaying

AbstractBecause of the surging demands of multimedia services, quality‐of‐experience (QoE) is becoming an important metric to evaluate network quality from users' perspective. In this paper, resource optimisation to achieve optimal tradeoff between QoE and energy consumption in bidirectional orthogonal frequency‐division multiple‐access relaying networks is addressed so as to provide satisfactory multimedia delivery quality and support green communications. We first formulate a QoE‐energy efficiency tradeoff optimisation where QoE requirements and relaying traffic balance are considered and prove that QoE‐energy efficiency is quasiconcave on QoE, which suggests the existence of a unique global optimal tradeoff point. We then propose an optimisation framework to achieve the optimal tradeoff efficiently. With the framework, we develop resource allocation approaches for two specific relaying strategies, that is, two‐phase decode‐and‐forward relaying with dynamic XOR network coding and compute‐and‐forward relaying with physical network coding via structured codes. Numerical results validate theoretical findings and demonstrate the effectiveness of the proposed optimisation solution for achieving the tradeoff between QoE and energy consumption. Copyright © 2015 John Wiley & Sons, Ltd.

Opportunistic scheduling and incentive mechanism for OFDMA networks with D2D relaying

The device-to-device (D2D) relaying is considered one of promising technologies to improve the spectral efficiency and extend the coverage of the cellular system with low additional costs. In the system with D2D relaying, some of user equipments (UEs) can act as relay stations (RSs) that forward other UEs’ data from/to the base station (BS). Compared with the RS, the D2D relaying has several advantages such as low deployment costs and high flexibility. We study an opportunistic subchannel scheduling problem in the OFDMA cellular network with D2D relaying in this paper. We formulate a stochastic optimization problem to maximize the sum-rate of the system with D2D relaying while satisfying the minimum average data rate requirement for each UE, and then develop an opportunistic scheduling algorithm by solving it. Due to a high computational complexity of the optimal scheduling algorithm, we also propose a heuristic algorithm with a lower computational complexity. In addition, since UEs that participate in D2D relaying sacrifice their resources to relay other UEs’ data, we also study incentive mechanisms to compensate their sacrifices. Through simulation results, we show the performance of our algorithms and the effects of our incentive mechanisms.

Performance Analysis of Asynchronous Multicarrier Wireless Networks

This paper develops a novel analytical framework for asynchronous wireless networks deploying multicarrier transmission. Nodes in the network have different notions of timing, so from the viewpoint of a typical receiver, the received signals from different transmitters are asynchronous, leading to a loss of orthogonality between subcarriers. We first develop a detailed link-level analysis based on OFDM, based on which we propose a tractable system-level signal-to-interference-plus-noise ratio (SINR) model for asynchronous OFDM networks. The proposed model is used to analytically characterize several important statistics in asynchronous networks with spatially distributed transmitters, including (i) the number of decodable transmitters, (ii) the decoding probability of the nearest transmitter, and (iii) the system throughput. The system-level loss from lack of synchronization is quantified, and to mitigate the loss, we compare and discuss four possible solutions including extended cyclic prefix, advanced receiver timing, dynamic receiver timing positioning, and semi-static receiver timing positioning with multiple timing hypotheses. The model and results are general, and apply to ad hoc networks, cellular systems, and neighbor discovery in device-to-device (D2D) networks.

A PDF/PMF Function Based Frequency Allocation Scheme in Fractional Frequency Reuse Aided OFDMA Networks

A novel frequency allocation scheme based on probability density/mass function functions (PDF/PMF) of random variables is proposed in this paper, which is capable of adjusting the balance between long term fairness and performance in fractional frequency reuse aided orthogonal frequency division multiple access based networks. This scheme divides the allocation process into two steps, including the intra-group allocation and the inter-group allocation. By adjusting the values of a set of parameters, such as rate parameters of PDF/PMF functions, and the ratio of radii of the center region and the whole cell, the presented scheme achieves a flexible adjustment between user-fairness and cell-throughput. Simulation results indicate that compared with the proportional fairness allocation and the equal rate allocation, the proposed scheme has significant performance advantage when the values of parameters are appropriate, and also has continuous controllability between "absolutely fair" and "absolutely unfair".

Joint Subcarrier Assignment and Power Allocation in Full-Duplex OFDMA Networks

Recent advances in the physical layer have demonstrated the feasibility of in-band wireless full-duplex which enables a node to transmit and receive simultaneously on the same frequency band. While the full-duplex operation can ideally double the spectral efficiency, the network-level gain of full-duplex in large-scale networks remains unclear due to the complicated resource allocation in multi-carrier and multi-user environments. In this paper, we consider a single-cell full-duplex OFDMA network which consists of one full-duplex base station (BS) and multiple full-duplex mobile nodes. Our goal is to maximize the sum-rate performance by jointly optimizing subcarrier assignment and power allocation considering the characteristics of full-duplex transmissions. We develop an iterative solution that achieves local Pareto optimality in typical scenarios. Through extensive simulations, we demonstrate that our solution empirically achieves near-optimal performance and outperforms other resource allocation schemes designed for half-duplex networks. Also, we reveal the impact of various factors such as the channel correlation, the residual self-interference, and the distance between the BS and nodes on the full-duplex gain.

Performance Evaluation of Mixed Traffic Schedulers in OFDMA Networks

Orthogonal Frequency Division Multiple Access based 4G cellular systems are designed to support different types of traffic through packet switching only. Hence, packet schedulers are important in i...

Network Coding for Intra-Cell Communications in OFDMA Networks

In this letter, we consider a new communication scenario in cellular networks, which is called intra-cell communications (ICC) , for which user pairs within the same cell exchange information through the base station (BS). A network coding based protocol is proposed to assist ICC in OFDMA networks to improve the spectral efficiency. In the uplink, each user accesses the BS following the OFDMA principle, while in the downlink, the BS transmits to each of the user pairs using the OFDMA principle. To do so, the BS performs bit level XOR (BLX) operation on the information bits received from each user pair. The output is then transmitted back to the same user pair through subcarrier sharing. We formulate the joint uplink/downlink subcarrier assignment and power allocation problem to maximize the weighted sum rate. While the formulated problem is non-convex, an asymptotically optimal, yet low complexity algorithm is proposed. Simulation results are presented to verify that the proposed protocol outperforms subcarrier pairing and assignment schemes which require no subcarrier sharing in both uplink and downlink.

Adaptive Sub-Carrier Level Power Allocation in OFDMA Networks

In today’s OFDMA networks, the transmission power is typically fixed and the same for all the sub-carriers that compose a channel. The sub-carriers though, experience different degrees of fading and thus, the received power is different for different sub-carriers; while some frequencies experience deep fades, others are relatively unaffected. In this paper, we make a case for redistributing the power across the sub-carriers (subject to a fixed power budget constraint) to better cope with this frequency selectivity. Specifically, we design a joint power and rate adaptation scheme (called JPRA for short) wherein power redistribution is combined with sub-carrier level rate adaptation to yield significant throughput benefits. We further consider three variants of JPRA: (a) JPRA-Basic where, the power is redistributed across sub-carriers so as to support a maximum common rate across all the sub-carriers (b) JPRA-Intermediate where, the power is redistributed across sub-carriers so as to support a maximum common rate across a “subset” of sub-carriers such that the aggregate rate is maximized. (c) JPRA-Adaptive where, the goal is to redistribute power such that the transmission time of a packet is minimized. While the first two variants decrease transceiver complexity and are simpler, the third is geared towards achieving the maximum throughput possible. We implement all three variants of JPRA on our WARP radio testbed. Our extensive experiments demonstrate that JPRA can provide a 35 percent improvement in total network throughput in testbed experiments compared to FARA, a scheme where only sub-carrier level rate adaptation is used. We also perform simulations to demonstrate the efficacy of JPRA in larger scale networks.